Structural analysis of zincocenes with substituted cyclopentadienyl rings

New zincocenes [ZnCp′2] (2-5) with substituted cyclopentadienyl ligands C5Me4H, C5Me 4tBu, C5Me4SiMe2tBu and C 5Me4SiMe3, respectively, have been prepared by the reaction of ZnCl2 with the appropriate Cp′-transfer reagent. For a comparative structural study, the known [Zn(C5H 4SiMe3)2] (1), has also been investigated, along with the mixed-ring zincocenes [Zn(C5Me5)(C 5Me4SiMe3)] (6) and [Zn(C5Me 5)(C5H4SiMe3)] (7), the last two obtained by conproportionation of [Zn(C5Me5),] with 5 or 1, as appropriate. All new compounds were characterised by NMR spectroscopy, and by X-ray methods, with the exception of 7, which yields a side-product (C) upon attempted crystallisation. Compounds 5 and 6 were also investigated by 13C CPMAS NMR spectroscopy. Zincocenes 1 and 2 have infinite chain structures with bridging Cp′ ligands, while 3 and 4 exhibit slipped-sandwich geometries. Compounds 5 and 6 have rigid, η5/ η1(σ) structures, in which the monohapto C 5Me4SiMe3 ligand is bound to zinc through the silyl-bearing carbon atom, forming a Zn-C bond of comparable strength to the Zn-Me bond in ZnMe2. Zincocene 5 has dynamic behaviour in solution, but a rigid η5/η1(σ) structure in the solid state, as revealed by 13C CPMAS NMR studies, whereas for 6 the different nature of the Cp′ ligands and of the ring substituents of the η1-Cp′ group (Me and SiMe3) have permitted observation for the first time of the rigid η5/η1 solution structure. Iminoacyl compounds of composition [Zn(η5- C5Me4R)(η1-C(NXyl)C5Me 4R)] resulting from the reactions of some of the above zincocenes and CNXyl (Xyl = 2,6-dimethylphenylisocyanide) have also been obtained and characterised. © 2009 Wiley-VCH Verlag GmbH & Co. KGaA.